Ion exchange polymers are useful in many applications, for example, making ion exchange membranes or coatings for ion separation processes. Common technique for producing ion-exchange polymers involves polymerization of a non-ionic, non-water soluble, di-ethylenic cross-linking agent, for example, divinyl benzene with a monomer such as styrene in a non-aqueous solvent such as diethyl-benzene. The resulting solid polymer, for example, in sheet or membrane form is equilibrated or washed several times with a solvent such as ethylene dichloride to remove and replace the diethyl-benzene solvent. Where cation exchange membranes are desired, the membranes are then reacted with a solution of sulfur trioxide and ethylene dichloride to form sulfonate groups which upon washing with methanol and neutralization with sodium bicarbonate gives the polymer strongly basic ion-exchange properties. The water insoluble monomers and the polymerization reaction and subsequent reaction carried out in non-aqueous solvents necessitate chemical disposal problems with attendant loss of the organic solvents.
Water-soluble cross-linking agents polymerizable in aqueous solvent systems have been developed to overcome the above-mentioned problems. Cross-linking of the polymer occurs by means of a condensation reaction between two monomers and takes place simultaneously with the polymerization, so no di-ethylenic monomers are required. At the same time, the expense of petroleum derived solvents and the problem of their disposal are eliminated.
However, most currently available water-soluble cross-linking agents are expensive and not environment friendly. In the meantime, some applications, e.g., supercapacitor electrodes, prefer polymers that have low resistance, low swelling ratio and good coating morphology and that can be coated to decrease the energy consumption and increase current efficiency of the electrodes.
Thus, it would be desirable to have a method for making a low swelling ratio polymer from water soluble, cheap and environment friendly materials and a method for coating an electrode with the polymer to reduce resistance and increase current efficiency of the electrode.